Shell Programming and Scripting

Thank you very much radoulov. If you could please explain the code lines would be very much helpful specially the use of _

awk:

Code:

nawk 'BEGIN{
n=1
flag=1
}
{
	if(NR==1)
		a=$0
	if(NR==2)
		b=$0
	if(NR>2)
	{
        	file=sprintf("a%s.txt",n)
        	if(flag)
		{
			print a >> file
			print b >> file
			flag=0
		}
        	print $0 >> file
		if((NR-2)%5==0)
                {
			n++
			flag=1
		}
	}

}' file

perl :

Code:

$flag=1;
$n=1;
open(FH,"<file");
while(<FH>){
	if($.==1){$a=$_;}
	if($.==2){$b=$_;}
	if($.>2)
	{
        	$file=sprintf("a%s.txt",$n);
		open(FH1,">>$file");
        	if($flag)
		{
			print FH1 $a ;
			print FH1 $b ;
			$flag=0;
		}
        	print FH1 $_;
		if(($.-2)%5==0)
                {
			$n++;
			$flag=1;
		}
	}

}
close(FH);

Sure.

Code:

NR < 3 { hd = hd ? hd RS $0 : $0; next }

Format the header: while reading the first two records: NR < 3, concatenate the first record, a newline and the second record using the ternary operator (if ? then : else). So the hd variable contains the header.

Code:

{ _ = _ ? _ RS $0 : $0; c++ }

While reading the rest of the input (because of the next statement in the previous action), concatenate the records using the same mechanism: there is nothing special in the _ character, it's a regular variable, I use it often as a default variable name (a bit like the Perl special variable _) and increment a counter variable c (I need it because of your requirement for the number of records in the last file).

Code:

!(++i % 5) && c > 2 {
  if (f) close("sub_" f)
  print hd RS _ > ("sub_" ++f)
  _ = c = 0
  }

When the remainder of the division of the incrementing i variable (++i) and 5 is not true (is 0), i.e. every five records,
and (logical) the value of the counter c is greater than 2 (if less than 3 records, continue with the current file), do the following:
close the previous output file (if exists), print to the new one: the header, a newline (RS), and the previously build content (the value of the _ variable). Clean the _ and the c variable at the end (set to 0).

Code:

END { print _ > ("sub_"(c > 2 ? ++f : f)) }

After reading the entire input if there are less than 2 records in the _ variable,
print them in the current file, otherwise, print them in a new one.

Hope this helps.